The present invention relates to ceramic cores for casting hollow metal castings and, more particularly, to a method of making ceramic casting cores having a controlled surface texture that will be imparted to internal passages of castings cast about the core.
Most manufacturers of gas turbine engines are evaluating advanced turbine airfoils (i.e. turbine blade or vane) which include intricate air cooling channels to improve efficiency of airfoil internal cooling to permit greater engine thrust and provide satisfactory airfoil service life. One approach being evaluated involves increasing the surface roughness of the internal cooling air passages to improve blade cooling efficiency.
An object of the present invention is to provide a method of making a ceramic casting core having a core surface with controlled surface texture that will be imparted to internal passages of a gas turbine engine blade or other cast component cast about the core.
The present invention provides in one embodiment a method of making a ceramic core wherein the ceramic core is grit blasted using abrasive grit media directed at the core through a preformed apertured mask or pattern to impart a controlled pattern of concavities (depressions) on the core surface by impingement of the abrasive grit media thereon while maintaining the desired overall core configuration or contour. Ceramic cores made by injection molding, transfer molding, or pouring can be grit blasted in this manner in the green (unfired) condition or in the fired condition. The apertured mask or pattern can comprise an apertured screen, woven or knitted cloth, paper, plastic or other material which can be temporarily adhered on the core.
The present invention provides in another embodiment a method of making a ceramic casting core wherein the ceramic core is formed in a molding die having a fugitive liner with a controlled surface texture positioned on the die surface for temporary incorporation on the core surface to impart a controlled surface texture thereto and subsequently removed from the core. Alternately, in another embodiment of the invention, the ceramic core is formed in a molding die having a textured die insert that remains with the die and imparts a controlled surface texture to the surface of the ceramic core as it is molded in the die.
The present invention is advantageous in that ceramic cores can be formed with a controlled surface texture or roughness morphology that is imparted to internal cooling air passages of a turbine blade cast about the core while maintaining the overall desired core configuration.